1. Field of the Invention
This invention is concerned with apparatus and a method for the identification of articles or objects.
2. Discussion of Prior Art
Conventionally, identification of articles has been achieved by the inclusion of features on the article which can be read by some means. These might include graphically complex features or holographic features. Such features however, have the disadvantage that their presence is obviously apparent and this is not always desirable
Furthermore, whilst such features can be easily identified manually, such as labels or holograms, they are more difficult to identify using automated systems. Bar codes are a commonly used machine readable identification means. However, bar codes contain a lot of information, and whilst suitable for certain applications, for example supermarket product sales, such readout systems are too slow for applications requiring very high speed identification of articles.
An object of the present invention is to provide a reliable means of identification which is not immediately apparent to the human eye and which is compatible with automated identification techniques and high speed readout systems.
It is an object of the present invention to provide a means for obtaining strong identification signals which are derived from physically robust features, created using materials which are acceptable for use on or in articles. In addition, the invention lends itself to high speed, automated checking. This is particularly advantageous when dealing with high volumes of articles.
According to the present invention apparatus for the identification of articles endowed with polarisation changing means for changing the polarisation properties of radiation incident on the article comprises,
a source of non-randomly polarised microwave radiation,
means for detecting the change in polarisation properties of the radiation.
The polarisation changing means may comprise means for changing the properties on transmission therethrough or reflection therefrom.
The microwave radiation may have a first plane of polarisation and the polarisation changing means may comprise means for changing the plane of polarisation to a second plane of polarisation. Preferably, the first and second planes of polarisation are substantially orthogonal.
The apparatus may comprise a transmitting antenna and a receiving antenna connected to suitable microwave radiation detecting means, the receiving antenna being arranged to favour reception of microwave radiation having the second plane of polarisation. At least one of the transmitting antenna and the receiving antenna may be a waveguide.
The polarisation changing means may comprise at least one feature having at least two pairs of dipole arms, wherein each pair of dipole arms is arranged to be substantially parallel to a different one of the first plane of polarisation or the second plane of polarisation, the feature being arranged on or within the article.
Alternatively, the polarisation changing means may comprise at least one feature having an edge oriented at a non-zero angle, xcex8, to a direction substantially parallel or substantially orthogonal to the first plane of polarisation. Preferably, the angle, xcex8, is substantially 45xc2x0. This provides the advantage that coupling of the microwave radiation having a first plane of polarisation to the waveguide connected to the detection means is maximised. For example, the one or more features may be a strip arranged on or within the article.
The polarisation changing means may comprise any one of a conducting foil, a conducting ink, a conducting oxide, a metal fibre or a carbon fibre. Alternatively, the polarisation changing means may comprise an insulating material.
The polarisation changing means may comprise covert means for preventing the changing of the polarisation properties by the polarisation changing means in one or more selected location, wherein the arrangement of the one or more selected location provides an identification code. For example, the polarisation changing means may comprise a plurality of features for changing the polarisation properties of the radiation, whereby one or more selected feature has applied thereto covert means for preventing the changing of the polarisation properties by the one or more selected feature or features. For example, the covert means for preventing the changing of the polarisation properties may comprise one or more layer of conducting material. This layer may be arranged substantially parallel to and in contact with the one or more features.
The apparatus may also comprise means for determining the orientation of the polarisation changing means. For example, the apparatus may comprise a Homodyne receiver having a transmitting antenna and a receiving antenna, arranged such that, in use, the polarisation changing means has a location between the transmitting antenna of the Homodyne receiver and the receiving antenna of the Homodyne receiver.
The polarisation changing means may comprise a plurality of features, at least one of the features being arranged to have a dissimilar orientation from the other feature or other features, whereby the arrangement of the feature orientations provides an identification code.
The apparatus may include both (i) means for determining the orientation of the means for changing the polarisation properties of the radiation and (ii) covert means for preventing the changing of the polarisation properties by the polarisation changing means. This has the advantage of providing a more complex identification code.
According to a second aspect of the invention a method for identifying articles comprises the steps of;
(i) endowing articles to be identified with polarisation changing means for changing the polarisation properties of non-randomly polarised microwave radiation,
(ii) illuminating articles to be identified with non-randomly polarised microwave radiation and
(iii) detecting a change in the polarisation properties of the radiation.
According to a third aspect of the invention, an article, for use in the apparatus or method of the invention, comprises
polarisation changing means for changing the polarisation properties of non-randomly polarised microwave radiation for identification purposes, wherein the polarisation changing means are suitable for arrangement on or within the articles to be identified.